This invention provides for metal surfaces which are derivatized when treated with .alpha.-.omega. bis-functionalized substantially linear aliphatic, including fluoroaliphatic, acids or salts thereof. These derivatized metal surfaces exhibit changes in surface properties. In particular, composites formed from polymers and metallic surfaces derivatized according to a process of the present invention exhibit surprising durability.
Wystrach (U.S. Pat. No. 3,770,514) discloses the application of diphosphine oxide derivatives to a metal surface followed by application of a coating to the so-treated surface. The coatings disclosed are paints and adhesives. Wystrach further discloses that a metallic surface treated first with an inorganic chromate and then the diphosphine oxide derivative exhibits enhanced corrosion resistance over prior art treatments. Wystrach's diphosphine oxide derivatives encompass structures containing up to four-carbon chains between phosphine groups, and a number of pendant groups on the phosphorus including hydroxy and hydroxyalkyl, with methylene bis[bis(hydroxymethyl)phosphine oxide] as the preferred species.
Hwa (U.S. Pat. No. 3,803,047 and U.S. Pat. No. 3,808,048) discloses compositions consisting essentially of certain alkylene polyphosphonic acids and a water-soluble zinc salt, and compositions consisting essentially of alkylene polyphosphonic acids and certain azole compounds and/or a water-soluble zinc salt. Ethanol 1,1-diphosphonic acid is disclosed as a preferred polyphosphonic acid.
Dines et al. (WO 87/01988) disclose "multi-layer structures" wherein a polymer composite layer is secured to certain metallic or polymeric substrates. The polymer composite layer is composed of a polymer selected from certain groups of polymers, and a particulate, layered compound selected from the group consisting of M(O.sub.3 ZO.sub.x R).sub.n compounds, as defined therein, preferably M(O.sub.3 PR).sub.2 or M(O.sub.3 POR).sub.2. The particulate, layered compound may be tailored to be compatible with the polymer and provide adhesion between such polymer and the substrate. The particulate, layered compound may be composited on the surface of the polymer, or homogeneously dispersed throughout the polymer.
Detloff et al. (U.S. Pat. No. 4,777,091) disclose the use of aminophosphonic acids, preferably multi-phosphonic acids, to prime surfaces of steel or galvanized metal, to take polyether resin-based coatings. The compositions taught are all relatively short-chain molecules, while long chain and branched molecules are disclosed. Detloff et al. are silent in regard to other types of coatings. Further, Detloff et al's teachings make no distinctions regarding chain lengths, degree of branching, or the desirability of .alpha..omega. diacids.
Wieserman et al. (U.S. Pat. No. 4,994,429) disclose the use of organic acid molecules, at least one end of which is a phosphorus-containing acid group, to form "active layers" on metal oxide/hydroxide particles to form active material. R groups linking the phosphorus-containing acid group to an unreacted group contain 1-30 carbon atoms. Uses of the active material disclosed include among others adsorbents and promoters for adhesive bonding, ceramics, and polymers. Wieserman is silent in regard to use of metals as substrates. Nothing is taught therein about any effects of chain length, and their examples are confined to relatively short chain lengths. There is no mention of neutralizing the "active" free acid end to generate binding sites for acid polymers.
Allara et al. (J. Am. Chem. Soc. Vol. 113, No. 5, p. 1852, 1991) disclose the treatment of metallic surfaces using an .alpha.-.omega. dicarboxylic acid having a carbon chain length of 30 carbons. The linear molecule is said to bend so that both ends of the chain contact the metallic surface, leaving the hydrocarbon backbone to impart a hydrophobic character to the surface so formed.
It is generally known in the art of forming self assembled monolayers of alkane thiols on gold that there is a transition from disordered to ordered molecular monolayers which occurs with increasing chain length (J. Am Chem. Soc., Vol. 109 (12) p. 3559, 1987). Yang et al (J. Am. Chem. Soc., Vol. 115 (25), p. 11855, 1993) teach that the degree of order of the backbone chains in metal alkyl bis(phosphonate) solids increases with chain length approaching a maximum when the chain is at least 11 carbon units long. The relative degree of organization is inferred from the location of CH.sub.2 bond stretches in the infrared spectrum of the material, which is said to shift to lower wavenumber with increasing organization. However, there is no teaching in that art to treat metallic surfaces to achieve improved adhesion of coatings, polymer films, or for improved corrosion resistance.